Precast concrete slab type structures are commonly used in constructing walls, floors, and concrete decks. They generally take the shape of concrete slabs which may have a t-shape in cross section. There is a horizontal portion of the slab which is the load bearing surface and there is generally reinforcing mesh or bars within the slab. There is at least one generally flat surface or edge that adjoins a flat surface or edge of a confronting adjacent slab.
When the concrete slabs are placed next to each other to form the wall or deck, it is possible for the slabs to move with respect to each other. This is due to wind forces or thermal expansion. In order to prevent or minimize the relative movement and to increase the strength of the final structure, metal inserts, often called “weldments” are place within the concrete slabs with a portion of the weldment extending out from an edge of the slab. When the slabs are positioned for final assembly, the metal weldment of one slab is aligned with and opposite to a complementary metal weldment in an adjacent slab. The metal complementary weldments are welded to each other to join the two weldments. This results in a unitary structure that is much stronger and less prone to movement than if no method of joining the slabs were used.
Various types of weldments have been used in the past. One such type is a U-shaped cylindrical reinforcing bar that had the arms of the “U” embedded within the concrete and the base of the “U” exposed along the edge of the concrete slab. Because the exact position of the arms could not be maintained when the concrete slab was poured, and the “U” shaped reinforcing bar did not have adequate means to keep it secured within the concrete slab, the reinforcing bar oftentimes pulled out from the slab when under load. Obviously this was unacceptable as it substantially weakened the overall structure.
An improved weldment is illustrated in U.S. Pat. No. 5,402,616. This weldment provides a weldment that has arms that support a reinforcing mesh within the concrete mold during the molding operation. The mesh is accurately positioned and retained in the proper position during the molding operation so that it buried in the concrete slab at a proper depth and a predetermined distance from the edge of the slab. However, a problem with this particular weldment, which is similar to the problem in the other prior art weldments, is securing the weldment within the concrete slab at all times. Horizontal and vertical forces tend to loosen the weldment within the slab which can eventually cause the weldment to be pulled out from the slab.
Another problem in the past was positioning the weldment into the mold that is used to form the concrete slab. Not only must the weldment be accurately positioned and have that position maintained when the concrete is poured, but the face of the weldment that is to be welded, must be kept relatively clean from concrete so that it is ready for welding. This presents additional problems during the casting process.
Thus, there is the need for a concrete weldment having improved securing properties over the weldments illustrated in the prior art that causes the weldment to be more securely retained within the concrete slab even when the weldment is subjected to vertical and horizontal forces. It is an object of the invention to provide a concrete having these properties, yet are not more expensive to manufacture than weldments of the prior art. There is also a need for an improved positioning mechanism to maintain the weldment in the proper position during the concrete casting process and further to keep the weldable face of the weldment as clean as possible. This results in an increased weldable area, at the proper angle to the concrete surface, and allows for thermal expansion of the weldment without cracking and spalling of the concrete.
Applicant's invention solves the problem stated above by designing a weldment that comprises a central plate which defines the weldable surface. The central plate is at an acute angle with respect to the horizontal plane of the concrete slab. There is a pair of outstanding arms extending out from the each of the ends of the central plate. Each of the outstanding arms has a top edge and a bottom edge. In one embodiment there is an irregular surface along the top edge of one or both of the outstanding arms. The irregular surface can be a v-shaped cut or a saw-tooth cut in the top edge. This irregular surface provides a locking or high friction surface against which the weldment locks into the concrete slab as the poured concrete hardens. The resulting locking edges of the arms further increases the force required to pull the weldment from the concrete slab as compared to those of the prior art.
Applicant's invention also provides for a cap or cover that is attached to the central plate prior to the casting process. The cap is further attached to the steel mold that defines the concrete slab. This cap covers the weldable surface and top and bottom edges of the central plate and accurately positions the weldment within the mold. After the concrete slab is poured and hardens, the cap is removed from the central plate, which presents a clean weldable surface. A recess is also formed in the concrete slab around the central plate to allow for thermal expansion when it is welded.